Ultimate Flange Selection Guide : SIX Common Flange Types Structure & Application Selection

Six mainstream flanges including WN, SO, BL, SW, TH, LJ dominate global piping projects under ASME B16.5 & EN 1092-1 standards. Wrong structure selection always causes extra procurement cost and hidden safety risk, detailed specification as below:

1. WN Weld Neck Flange: Tapered long hub with full penetration butt weld, max rating up to Class2500, excellent thermal & pressure resistance, widely applied in refinery, power plant and critical flammable fluid pipeline with higher cost.

2. SO Slip On Flange: Pipe slides into flange bore with double fillet weld, cost-effective & easy installation from Class150 to Class300, top choice for water supply, HVAC and general low-moderate pressure chemical piping, most popular in global market.

3. BL Blind Flange: Solid blank disc for pipe end closure & future expansion, available for all pressure classes, essential spare part for every engineering project maintenance.

4. SW Socket Weld Flange: For small bore DN≤80 only, pipe inserted into counterbore then welded, better tightness than SO, Class300~600 standard for instrument and small high-pressure gas piping.

5. TH Threaded NPT Flange: No welding needed with internal NPT thread, perfect for explosion-proof gas pipeline construction, not suitable for cyclic high temperature service.

6. LJ Lap Joint Flange: Split design with stub end + loose backing flange, rotatable flange for easy bolt hole alignment. Users can use expensive stainless steel stub end & cheap carbon steel flange to cut cost on corrosive medium piping with frequent disassembly requirement.

Quick selection rule: WN for critical high-pressure service; SO for general low-pressure project; BL for end blocking; SW for small bore high-pressure; TH for non-weld explosion-proof; LJ for corrosive frequent-maintenance piping. We are China OEM flange forging factory for non-standard customized sizes.

Six mainstream forged flanges including WN, SO, BL, SW, TH and LJ are widely used in global industrial piping systems. They differ greatly in structure, welding method, pressure resistance, cost and applicable working conditions, which often causes wrong purchase and on-site assembly troubles for pipeline engineers and buyers.

1. Weld Neck Flange (WN): Integral forged with tapered hub, full penetration butt weld connects pipe and flange continuously. Its intact metal grain flow enables high pressure rating from Class150 up to Class2500 with excellent resistance to high temperature and thermal shock. Mainly applied in refineries, thermal power plants, LNG and flammable oil & gas high-pressure pipelines. It has the highest production cost among six types due to complicated forging and machining.

2. Slip On Flange (SO): Pipe inserts into flange bore and fixed by double fillet welding. Low processing cost and easy installation with pressure Class150-Class300 make it the most popular flange worldwide. Suitable for municipal water supply, HVAC, ordinary chemical and waste water treatment medium-low pressure piping.

3. Blind Flange (BL): Solid blank disc without bore for pipe end blocking, pipeline isolation during maintenance and reserved expansion interface. Available for all pressure classes and indispensable spare parts for tank nozzle and pipe network partition in all engineering projects.

4. Socket Weld Flange (SW): Specially designed for small bore DN15-DN80, pipe is inserted into counterbore then welded for better sealing than SO flange, rated Class300~600. Ideal for instrument tubing, hydraulic pipeline and small-bore high-pressure fine chemical piping.

5. Threaded Flange (TH, NPT): Connected by NPT thread without any hot welding, excellent for explosion-proof construction such as natural gas small pipeline. Not recommended for piping with frequent temperature fluctuation.

6. Lap Joint Flange (LJ): Composed of stub end and loose flange ring, the ring can rotate freely to align bolt holes conveniently. For corrosive medium, expensive stainless steel stub end matches low-cost carbon steel flange to save budget, perfect for seawater pipeline and equipment nozzles requiring frequent disassembly.

Selection Tip: WN for critical high-risk piping; SO for general low-pressure project; BL for end closure; SW for small bore instrument line; TH for non-weld explosion-proof service; LJ for corrosive & frequent-maintenance pipeline. We are professional OEM flange factory supporting custom non-standard specification and special material production.